Effective Blade Inspection Plans Involve Advanced Planning and Method Selection
As the warmer weather is waning for most wind farms here in the U.S., the window for efficient blade repair service is quickly drawing to a close. This is because the blade repair guys don’t like to get cold and will soon be heading out to the Bahamas for an all winter party.
The main reason that blade repairs are a mostly seasonal service is because the materials used for repair are temperature sensitive. Some materials that can cure in a few hours in 80 degrees can take days to cure in temperatures below 70 degrees. Although we can help the cure along by applying heat, this process consumes more time, and as they say — time is money. This process is just not as efficient as it is in warmer weather.
So, what about blade inspections? Did you get a chance this summer to look at them all? How did you do it? Are you still unsure if the process you use is adequate? Blade inspections can be completed in many different ways, and each of these ways has its pros and cons. Let’s take some time here to discuss a variety of the most common ways blades are inspected. Remember, the main reason for blade inspections is to find problems, so you can decide what to do next — whether that is to run another season, to make repairs, or to take out of service.
Blade inspections should be happening on a continual basis with the personnel on site. To start, anyone that is near a wind turbine should be at least listening to the sounds it is making. Blades that have strange noises coming from them may be indicating that they have issues. Typically all three blades will make the same type of noise when the rotor is spinning so you have three blades to compare against each other. If one is making a different noise, then it is fair to assume that something is different and you may want to take time to further investigate.
Noises that should attract your attention are a blade whistle, or a ripping noise. A ripping noise is similar to the sound of a piece of paper being ripped. Both noises can indicate issues with the blade. Sometimes the source of the noise cannot be easily found. Other times the noise could be from a lightning strike, or simply from a torn piece of leading edge tape. While the lightning strike damage may be worth the time to repair, you may just let the torn tape go until it is worth dealing with.
Usually the first line of defense in blade inspection is your maintenance team. Again, when these personnel are near a turbine, they should be listening to the noise it makes. Additionally, if your turbine is stopped or pin wheeling, you should scan the blades with your binoculars (every truck has a set, right?).
The next cost-effective inspection is by blade-savvy teams that can come in and perform a ground-based inspection. These teams are experienced in knowing what to look for. They typically use spotting scopes or binoculars, and cameras with high-powered lenses. They first perform an inspection in the field, and then they take photos of the entire blade surface. They later review the high-resolution photos, using zoom capabilities to get a “close-up” view of the blade skin surface and inspect for damage.
Sometimes an even closer look is needed to determine suspicious points on a blade. This calls for an “on blade” inspection. There are two and a half ways to do this today. The first is by using a rope access team; secondly, using a cable-suspended basket. The “half” way is by utilizing the new drone-mounted aerial remote viewing cameras. I call this inspection method a “half” way because even though you can get right up to the damage with the drone, your physical access is still limited. You lose the ability to tap or poke at the blade surface that you have with the other methods. The drone, or quad copter, remote camera is a great example of how technology keeps helping us perform our work better. It is a great way of morphing between ground-based inspections and on-turbine inspections. These remote camera inspections are being performed by service companies, forward-thinking site technicians who own their own drone, as well as by entrepreneurs trying to make a focused business by utilizing this great new device. The only problem is, this new tool has raised the concern of the government as to whether or not they should be controlled. I think new technology always does that.
Having a team of techs on the blade is pretty expensive and is usually the last resort. But once a tech is there, he may be able to make the repair on the spot. I personally think that if I am going to put a tech on a blade, he better be able to make the repair. I feel I can get a good sense of the damage from ground-based and remote camera photos. Once the damage is found, I can determine, for the most part, if a repair is needed. Very rarely have I had to go on-blade to confirm an issue, but it has happened.
One point of the blade inspection work we should think about is the timing. Since most blade inspections require the sharing of extremely large amounts of data consisting of photos and the results of analyzing these photos. This data review takes time. From the data review we will typically get a request for more in-depth inspection or repairs. To get this additional work completed takes time, budget, and resources. Although a person can be quickly trained to inspect for blade damage, it takes time to train a person to properly access a blade and to make a repair.
Since this all takes time, and in the U.S. we are all experiencing the summer during the same time, most of us are competing for these limited blade repair resources. My recommendation is to get your scheduled inspections lined up early in the summer so that you can get the blade repair techs to your site before the colder weather hits. Otherwise you can get in line for the repair teams, potentially miss the window of repair for the warm months, and get stuck paying for inefficient repairs in the colder months… if at all.
Hopefully you were able to manage your blades well this past wind season like a pro. If not, there is always next year to improve your process and to reduce your costs. Don’t wait until summer to plan work on this.
As always work as safe as possible and work to prevent surprises.
About The Author
Jack Wallace is a veteran of wind farm operations and maintenance with more than 30 years of industry experience, and he is the Western business development manager and technical adviser for Frontier Pro Services. Wallace has taught wind turbine theory of operation and related subjects for various institutions in the U.S. and South Korea, and he is listed as an inventor on more than nine patents, all related to technology in the wind energy industry. He can be reached at firstname.lastname@example.org for questions or comments.